The invention relates to methods for the treatment, alleviation or prevention of lesions, especially ulcers, and in particular to means for use in any said method.
The term xe2x80x9clesionxe2x80x9d is used herein to mean any interruption in the surface of the skin or in the surface of a membrane lining any cavity within the body, whether resulting from injury or disease. The term xe2x80x9culcerxe2x80x9d is used herein to refer to any breach on the surface of the skin or on the surface of a membrane lining any cavity within the body, which does not tend to heal quickly.
Human skin is a complex integration of different types of cells and tissues which form an organ. Skin is also the primary seat of the sense of touch and creates a covering for the protection of the deeper tissues. The skin also plays an important role in the regulation of body temperature and is also an excretory and absorbing organ. Skin consists primarily of a layer of vascular tissue and an external covering of epithelium known as the epidermis. Near the surface are the sensitive papillae, and alongside or imbedded beneath it are certain specialised organs, specifically the sweat glands, hair follicles, and sebaceous glands.
In order to protect the tissues below from trauma, the skin must be tough, flexible, and highly elastic. In the context of this function, injuries to the skin can occur. Wounds, which are caused by physical means, result in a disruption of the normal continuity of the structures of the skin. Examples of wounds include cuts, punctures, lacerations, etc. There are two types of healing processes:
(1) primary union or first intention healing and
(2) secondary union or second intention healing.
Primary union occurs when a clean wound with a minimal loss of tissue heals together cleanly. The process involves clotting and formation of a crust or scab to seal the wound; an acute inflammatory reaction, reepithelialization of the surface and fibrous bridging due to fibrin followed by complete sealing of the wound by an epithelial covering. Thereafter, hair follicles, sebaceous glands and sweat glands may subsequently regenerate. The process of second intention healing requires the removal of necrotic debris. The gap in the wound then fills in with fibrous materials. Second intention healing can be impaired by infection and by a restriction, for whatever reason, of the blood supply and therefore oxygenation status of the wound to give rise to ulcers. This invention is concerned, inter alia, with the treatment of those ulcers, which are exemplified by decubitus ulcers, described below.
In nursing homes, hospitals or in private homes where invalid patients with certain diseases and afflictions are bedridden, a problem arises from bed sores which these patients develop. These bed sores, which have a tendency to ulcerate and may also be known as decubitus ulcers, usually result from a loss of blood circulation caused by pressure on the skin, particularly pressure over a bony protuberance. Decubitus means ischaemic necrosis of the skin or subcutaneous tissue caused at a projected bone area due to continuous pressure. It is commonly developed in aged patients as a result of such patients being confined to their beds over long periods of time, and may also be developed on compression in plaster upon fracture.
Decubitus ulcers are defined by reference to four xe2x80x9cStagesxe2x80x9d according to severity: Stage Ixe2x80x94Skin pink-mottled, the epidermis is damaged; Stage IIxe2x80x94Skin is cracked, blistered and broken, the epidermis is destroyed; Stage IIIxe2x80x94Skin is broken with some tissue involvement, the sub-cutaneous skin is destroyed and there are decaying cells; Stage IVxe2x80x94Extensive penetration to muscle and bone, presence of necrotic tissue, and profuse drainage, structures are decayed. By stage III or IV, debridement is usually necessary.
The pressure on areas of support may exceed the mean capillary blood pressure, with the result that those areas are vulnerable to the formation of decubitus ulcers. Other factors which can contribute to formation of decubitus ulcers are lack of proper ventilation, moisture and diet. Additionally, the problem of bed wetting and the accumulation of urine in the bed contribute to the formation of bed sores since the moisture remains in the area of the patient""s body. Attempts have been made to remedy these conditions and thereby prevent the decubitus ulcers. Some have involved merely the passing of air through the bed mattress which air is then allowed to pass upwardly around the patient""s body. Other devices have had pulsatingly inflatable air mattresses which again merely allow the air to be circulated upwardly around the body of the patient. Those attempts have been relatively unsuccessful in practice.
Some supportive measures used for the prevention or alleviation of decubitus are: occupational therapy, physical therapy, and nutritional therapy. For example, it is the practice to change the position of a patient or to release one or more pressed areas of the patient from pressure so that his skin is protected from continuous compression. Typically, that involves a repositioning schedule every two hours, checking bony prominences for breakdown daily, keeping skin dry and clean, ambulating the patient as much as possible, forcing fluids, and using cornstarch to prevent friction. Other known practices are use of a special bed having a hygroscopic cushioning material and effecting rigorous skin cleaving and wiping, with the object of keeping the skin dry and thereby preventing secondary infection. Where the condition of decubitus is extremely serious, surgery is effected to resect the decubital part and then to restore the resulting lost part by sutured minification, adjacent flap, distant flap or the like.
There are many different products available for the care of decubitus ulcers, including solutions having antibacterial or antacid activity, water-repellent ointments, and dressings. For example, Betadine solution rinses are used for their antibacterial properties, but some allergic reactions can occur to the iodine, enhancing the skin problem. Uniwash and Uniderm treatments have to be done every eight hours or more frequently. Dressings are necessary and beneficial but sometimes tear the skin further. Medicated dressings such as Silvadene have to be changed also every eight hours. Domeboros Solution is used every four hours during the day. Antacids may be beneficial for superficial ulcers, but can hold in purlent matter and debris in the deep ulcer.
Patients particularly prone to formation of decubitis ulcers are cachetic patients (those in negative nitrogen balance), patients with congenital or acquired boney deformities, stroke patients who are immobile, paraplegics with uncontrollable muscle spasms, any spinal cord injury patient, incontinent patients, arthritic patients, those who are confused or comatose, nutritionally deficient patients, those with oedema or poor capillary refill, anyone who is on medications such as steroids, tranquilizers and analgesics, any geriatric patient, and anyone with pre-existing diseases. Decubiti in such patients may also result from or be exacerbated by friction, shearing force and pressure, which all hospital patients are exposed to while in bed. Usually, a combination of two of those forces will cause a pressure sore, which may appear within twelve hours. Friction can be from moving in bed, shearing can be from a position in bed, and pressure can be from gravity alone. A pressure of greater than 25 mm Hg. will occlude flow of blood to capillaries in soft tissues causing hypoxia and, if unrelieved, eventual necrosis which is manifested in decubitis ulcer formation.
Decubitus remains a skin disease which is difficult to prevent in patients who are immobile for a substantial length of time, even with intensive nursing attendance. Whilst the causes, observable symptoms and modes of treatment of ulcers in other membranes may differ substantially from those of decubitis, a common factor is the tendency of ulcers not to heal, or to heal only very slowly. Moreover, once ulceration has occurred, it remains difficult to cure, and can result in long and severe pain to patients. There remains a need for improved means of treating, alleviating and preventing the formation of ulcers, especially decubitis ulcers, as well as other types of lesion, for example, neoplastically transformed lesions, other lesions that may be virally infected, and warts.
The invention provides a composition for use in the treatment of lesions of the human or animal body, the composition comprising XOR and a pharmaceutically acceptable electron donor system. Xanthine oxidoreductase exists in two inter-convertible forms, xanthine dehydrogenase (XDH, EC 1.1.1.204) and xanthine oxidase (XO, EC 1.1.3.22). XDH, which is believed to predominate in vivo, preferentially reduces AND+, whereas XO does not reduce AND+, preferring molecular oxygen. Where reference is made herein to xe2x80x9cXORxe2x80x9d, that term includes xanthine oxidoreductase, which is to be understood as referring to both xanthine dehydrogenase (XDH) and xanthine oxidase (XO), where appropriate. It will be appreciated that references to XOR further include references to analogs of xanthine oxidoreductase that have xanthine oxidoreductase activity. Such analogs may include but are not limited to, for example, xanthine oxidoreductase which has been modified chemically or otherwise, analogs having fragments of xanthine oxidoreductase derived from naturally-occurring enzyme, and analogs having polypeptides obtained by replication of the enzyme or a portion thereof using any suitable biotechnological method, provided in each case that the catalytic activity of the endogenous xanthine oxidoreductase is retained at least to an appreciable extent.
References herein to xanthine oxidoreductase are furthermore to be understood as embracing material of any biological origin, for example, of mammalian or other animal origin, or originating from a suitable micoorganism, for example, aspergillus sp. Xanthine oxidoreductase of ruminant origin offers the advantage of ready availability.
The inventors have found that, unexpectedly, compositions according to the invention containing XOR and a pharmaceutically acceptable electron donor system have antiseptic properties and recuperative activity which will render them suitable agents for use in the treatment of lesions, including ulcers, for example, decubitus ulcers, ischaemic leg ulcers, diabetic foot ulcers, genito-urinary ulcers, ulcerative keratitis and ulcers of mucosal surfaces of the mouth and the like, neoplastically transformed lesions, virally infected lesions, warts, and lesions of the mucous membrane. Whilst the mode of action of the compositions is not known with certainty, it is believed that they may assist in the formation of granulation tissue in such conditions. Moreover, at least in the case of patients affected with decubitus ulcers, ischaemic leg ulcers, diabetic foot ulcers, genito-urinary ulcers and ulcerative keratitis and the like, it is believed that the compositions assist in increasing the local perfusion.
The enzyme xanthine oxidoreductase is a complex molybdoflavoprotein, the action of which has been studied for many years. It is a major protein component of the membrane surrounding fat droplets in whole milk. Consequently, cows"" milk is a rich and convenient source of the enzyme. Xanthine oxidoreductase has also been characterised from rat, chicken and turkey livers. Human milk has also been found to contain xanthine oxidoreductase.
In the treatment of ulcerative lesions, especially decubitus, it may be preferred for the composition to be used in combination with means for enclosing in airtight manner the lesion with the applied composition.
The composition of the invention may comprise one or more pharmaceutically acceptable excipients or carriers. The composition of the invention may be suitable for topical administration. Advantageously, the composition is suitable for topical application to the skin. The composition may advantageously be suitable for topical application to the cornea.
The composition may be used in a prophylactic method for the prevention of ulcers, or in a method of treatment of ulcers, especially decubitis ulcers. As already mentioned, the compositions of the invention may be used in the treatment of ulcerative keratitis. It has been found that small amounts of xanthine oxidoreductase may naturally be present on the cornea, the enzyme apparently being secreted from the lachrymal glands. The amount of enzyme secreted in a diseased eye is reduced, but may in accordance with the invention be augmented by application of a composition comprising XOR and an electron donor system.
The inventors have also found that small amounts of xanthine oxidoreductase are produced in the salivary glands and secreted in the mouth, and it is thought that the enzyme may play a part in defending the mucosal surfaces of the mouth from infection. The composition of the invention may be effective in the treatment of ulcers of the mucosal surfaces of the mouth.
The composition may be used in the treatment of neoplastically transformed lesions. The composition may be used in a prophylactic method for the prevention of, or in a method of treatment of, cervical cancer. As is well-known, cervical cancer is generally preceded by the occurrence of neoplastically transformed lesions which, if left untreated, in a large proportion of cases lead to development of cervical cancer. The inventors have found that xanthine oxidoreductase is naturally present in the healthy cervix. It is thought that the enzyme, generation of which varies with polymorphisms in the gene, may play a role in the prevention of infection in the cervix. The generation of the enzyme may be inhibited where a viral infection does occur. The diminished production of enzyme in situ may thus, in accordance with the invention, be augmented by application of a composition comprising XOR.
The invention further provides a dressing for application to a part of a human or animal body, comprising a substrate and a pharmaceutical composition retained on a surface of or within the substrate, the pharmaceutical composition comprising XOR and an electron donor system. Advantageously, the dressing comprises a layer of material which is impermeable to air, that is, which, when in use the dressing is applied to the part of the human or animal body, substantially prevents the passage of ambient air through the dressing to the said part.
There have been suggestions that xanthine oxidoreductase has a role in the production of bactericidal agents. In the presence of oxygen, xanthine oxidoreductase can catalyse the production of superoxide and hydrogen peroxide, which are known bactericidal agents. Bactericidal levels of superoxide or hydrogen peroxide are, however, unlikely to be attained at low oxygen concentrations.
It has been reported, Millar, T. M. et al, FEBS Letters 427 (1998) 225-228, that, under hypoxic conditions and in the presence of NADH, XOR is capable of catalysing the reduction of glyceryl trinitrate (GTN), as well as inorganic nitrate and nitrite, to nitric oxide (NO).
Nitric oxide (NO) is widely recognised as mediating the relaxation of smooth muscle in vasodilation and as initiating many other important biological functions, including inhibition of platelet aggregation and adhesion. Its generally accepted physiological source is NO synthase, a complex enzyme which is totally dependent on oxygen as one of its substrates for its activity and consequently ineffective in a hypoxic environment, where the vasodilatory properties of NO might be seen to be advantageous.
Hypoxic conditions may be present in some types of lesions, in particular, where the supply of oxygenated blood may be disrupted or prevented and/or where the lesions are enclosed in airtight manner, for example, using a dressing that is impermeable to air. In neoplastically transformed lesions of the cervix the conditions may also be hypoxic, the cervix having an intrinsically relatively low oxygen concentration.
We have found that the optimum pH for the production of NO from XOR under hypoxic conditions is about pH 5.5. Thus, we have found that lesions, especially ulcers, present an environment in which the production of NO in the presence of XOR would be at or near a peak.
At pH levels above about 4 pathogenic bacteria are more active than at lower pH values. It is postulated that, under conditions prevailing in lesions, especially ulcers, XOR can catalyse the production not only of superoxide, but of NO. Superoxide and NO rapidly interact to generate peroxynitrite, a much more potent bactericidal species than superoxide, NO or hydrogen peroxide. While superoxide has some bactericidal properties and in some situations NO has also been found to kill or damage bacteria, it is the interaction of superoxide and NO to form peroxynitrite and other products which is believed to give superior bactericidal action. Peroxynitrite (and, it is thought, other products of the interaction of superoxide and NO) are particularly potent bactericidal species.
The concentration of nitrite present in lesions is normally low, and it might therefore be thought that the potential for XOR-catalysed generation of NO would be limited. It is believed however that, the known affinity of XOR for acidic polysaccharides such as those occurring in bacterial capsules causes XOR to become more concentrated in the immediate vicinity of bacteria. In anaerobic environments, bacteria commonly are found to excrete nitrite and thus the association of XOR with the bacteria may have the result that the XOR will be located in a localised region of elevated nitrite concentration.
Whilst it is thought that it is the peroxynitrite formation that gives rise to the desirable bactericidal action of XOR in hypoxic conditions, it may in certain applications, for example, ulcerative keratitis be superoxide that is the predominant bactericidal species. In some circumstances, it will be desirable to maintain or promote a hypoxic environment in the region of application of the XOR-containing composition, thereby favouring the peroxynitrite pathway, whilst in others, such as in the treatment of ulcerative keratitis that may be unnecessary or even undesirable.
From the above it will be appreciated that the active XOR may be regarded as a xe2x80x9cnatural antibioticxe2x80x9d, that is, a substance of natural origin which is capable of destroying or inhibiting the growth of at least some strains of pathogenic micro-organism.
The substrate may itself constitute the impermeable layer. Preferably, the dressing comprises a substrate layer and an impermeable layer to which the substrate layer is attached. It will be appreciated, however, that the dressing of the invention will not necessarily include means for airtight sealing, it being possible for such sealing means to be provided separately, for example, in the form of an impermeable plastics film or a conventional airtight dressing. Advantageously, the substrate is an absorbent material. The substrate may be of any suitable material that is dermatologically acceptable. It will be appreciated that it will be desirable for the dressings to be sterile when applied to the body. Accordingly, the substrate should be one that will withstand any sterilisation method to which the dressing will be subjected, and the substrate material will thus be selected having regard to the sterilisation method to be used. Advantageously, the substrate comprises collagen or freeze-dried calcium alginate. The substrate may be collagen fibril matting.
Advantageously, the xanthine oxidase is present in an amount of about 0.1 xcexcg to 1 mg, preferably 10 xcexcg to 1 mg, per g of the substrate.
In the compositions or dressings according to the invention, the xanthine oxidase is advantageously in lyophilised form. It will be appreciated that the method of isolation of the XOR for use in accordance with the invention will need to be so selected that the activity of the XOR is wholly or at least substantially retained. In general, such methods should not include any step in which the temperature of the XOR exceeds 65xc2x0 C. Advantageously, the electron donor system comprises at least one nitrogen-containing compound, which may be a heterocyclic compound. The nitrogen-containing compound may advantageously be selected from the group consisting of purines, nicotinamides, and derivatives thereof. Examples of suitable electron donors are NADH and hypoxanthine. There may also be an electron acceptor system present, for example, the composition may include one or more compounds selected from organic or inorganic nitrates and nitrites, for example, glyceryl trinitrate or isosorbyl dinitrate.
The invention also provides a method for the treatment of lesions, for example, decubitus, ischaemic leg ulcers, diabetic foot ulcers, genito-urinary ulcers and ulcerative keratitis and the like in a patient, which comprises administering to said patient a pharmaceutical composition comprising an effective amount of xanthine oxidase and a pharmaceutically acceptable electron donor system, wherein the method of administration comprises bringing the pharmaceutical composition into contact with the ulcers of said patient and effecting substantially airtight sealing of the ulcer and the composition in contact therewith from the ambient atmosphere. Advantageously, the composition is impregnated into a suitable packing substrate. The substrate may be selected from freeze-dried calcium alginate or collagen fibril matting.
The dosage administered will be dependent upon the age, health and weight of the recipient, kind of concurrent treatment, if any, frequency of treatment and the nature of the effect desired. For example, dosage forms for topical administration include about 0.1 xcexcg to 1 mg, and advantageously 10 xcexcg to 1 mg, of xanthine oxidase per gram of carrier. The dosages in the treatment of lesions other than ulcers may be similar to those required for ulcers. The composition may be in the form of a cream, gel, solution (including an injectable solution), ointment or any other suitable form, according to the nature and location of the lesion to be treated. The composition may advantageously be in the form of a gel that liquefies at body temperature. Such a gel may, for example, be pplied to an alginate substrate before application to the lesion to be treated, or may be incorporated into a dressing. The XOR may be present in those dosage forms in an amount of 0.1 xcexcg/ml to 1 mg/ml and preferably 10 xcexcg/ml to 1 mg/ml. The composition may contain other active ingredients, if desired. In the case of treatment of the cornea, it may be appropriate for the composition to be included in, for example, a lubricant solution administrable as eye drops.
Before the impregnated material is applied to a patient, it is preferable to wash the sore with a suitable washing compound. In practice, the composition and dressing of this invention will normally be used only after removal of any necrotic tissue that is present. Proper removal of necrotic tissue will normally be done under the supervision of a physician and may include surgical debridement.
The invention further provides a system for use in the treatment of lesions, having at least two components, a first component of the system comprising XOR and a second component of the system comprising an electron donor system, said first and second components being arranged for application to a surface of an animal or human body in combination or separately, simultaneously or sequentially.
The compositions and dressings of this invention have many advantages because of their combination of ingredients and the minimal accompanying treatment of the patient that is required. It is believed that the properties of the packing that are beneficial are as follows: antiseptic action through the generation of superoxide, nitric oxide and peroxynitrite by the enzyme xanthine oxidase, tonal, topical stimulation giving rise to increased circulation at the base of ulcers leading to increasing granulation tissue and thus accelerated healing.